For this type of pulse oximeter, on the premise that it is always worn, there has been proposed a ring-type pulse oximeter configured to press a measurement object portion to increase pulsation of arteries, for example, if there are few detectable pulsation components, or if vasoconstriction caused by low body temperature reduces measurement accuracy of oxygen saturation, or in similar cases (refer to Patent Literature 1).
Alternatively, there has been proposed an apparatus configured to simultaneously and continuously measure blood pressure and blood oxygen saturation, by obtaining a blood pressure value on the basis of the pulsation component and cuff pressure of one of two volume signals according to lights with different wavelengths, and by obtaining blood oxygen saturation from volume pulse wave signals extracted from respective pulsation components of the two volume signals (refer to Patent Literature 2).